Hallux valgus is characterized as a deformity of the great toe (hallux) and first metatarsophalangeal joint, wherein the first metatarsal is medially deviated, the great toe is laterally deviated and/or rotated on the head of the metatarsal, the plantar pad and sesamoids are displaced with the toe, and the ligaments on the medial side of the metatarsophalangeal joint are stretched. The position of the great toe with respect to the second toe can be overriding, underriding, abutting, or without contact. Thus, hallux valgus can involve transverse plane deformities (hallux abductus), or frontal and transverse plane deformities (hallux abductovalgus). With respect to deformities in the transverse plane, the angle between the longitudinal axis of the metatarsals of the first and second toes (intermetatarsal angle) typically deviates beyond the normal range of 8-12°. With respect to deformities in the frontal plane, the angle between the longitudinal axis of the metatarsal and proximal phalanx of the great toe (hallux valgus angle) typically deviates beyond the normal upper limit of 15-20°.
In addition to physical deformity, hallux valgus is often accompanied by formation of a callous, bursa, or bunion over the first metatarsal head, pain in the first metatarsophalangeal joint during ambulation, pain in the metatarsal head, and combinations thereof.
Hallux valgus is estimated to affect more than 43 million people in the United States, with incidence more predominate in females, those older than 60 years of age, teenagers who wear high heels, and athletes. It can develop due to numerous factors, including biomechanical instability (e.g., excessive protonation), arthritic/metabolic conditions (e.g., osteo/rheumatoid arthritis), neuromuscular disease (e.g., multiple sclerosis), trauma (e.g., soft-tissue sprains, dislocations, and sports-related injuries), and structural deformities (e.g., abnormal metatarsal length). Additionally, there tends to be familial disposition to developing hallux valgus.
Development of hallux valgus typically occurs in four stages. See Root, M L, “Normal and Abnormal Function of the Foot,” Vol. 2, Clinical Biomechanics (1977). The first stage is associated with lateral subluxation (partial or complete dislocation) of the proximal phalanx. The second stage is associated with increased abduction of the hallux in the transverse and/or frontal planes. The third stage is associated with additional subluxation at the first metatarsophalangeal joint. The fourth stage is associated with dislocation of the first metatarsophalangeal joint.
Hallux valgus is a complex deformity and various approaches to treating or correcting the deformity may be available. For example, when hallux valgus is in its early stages, or where surgical correction is contraindicated, braces, straps, splints, orthotics, or combinations thereof may be used to manage progression of the deformity and relieve the associated symptoms. However, surgery is the only means of correcting the deformity.
The first surgical treatment to address hallux valgus dates to 1881 when an osteotomy procedure involving an incision medial to the extensor hallucis longus, followed by incision of the periosteum, removal of exostosis, removal of bone from behind the caputulum of the metatarsus, and suturing of the bone. Since this forerunning procedure, numerous other procedures have been developed, all with the goal of addressing the deformity with minimal complications. Such surgical procedures, while varying depending upon the nature of the deformity and particular needs of the patient, generally allow for establishment of a congruous first metatarsophalangeal joint, reduction of the intermetatarsal angle, realignment of the sesamoids, realignment of the hallux to a rectus (rather than an abductus) position, and maintenance or increase of the range of motion of the first metatarsophalangeal joint.
Typical surgical procedures involve one or more of osteotomy of the metatarsal head, osteotomy of the metatarsal shaft or base, fusion of the metatarsophalangeal joint, resectional arthroplasty, resectional arthroplasty with a partial (hemi) implant, and resectional arthroplasty with a total implant. With respect to procedures involving an implant, numerous devices for use therewith are known in the art. For example, known hemi arthroplasty devices, which are typically used when the proximal phalanx is degenerated but the metatarsal head is intact, include the BioPro® hemi toe implant (BioPro, Inc., Port Huron, Mich.); Futura™ Metal Hemi Toe implant (Tornier, Edina, Minn.); K2™ Hemi Toe Implant System (Integra LifeSciences Corp., Plainsboro, N.J.); and Swanson™ Great Toe Implant (Wright Medical Technology, Inc., Arlington, Tenn.), all of which are depicted in FIG. 1A. Examples of known double-stemmed hinges, which are typically used when both the proximal phalanx and the metatarsal head are degenerated, include the Swanson™ Flexible Hinge Toe implant (Wright Medical Technology, Inc., Arlington, Tenn.); GAIT Implant™ (Sgarlato Med, San Jose, Calif.); and Futura™ Flexible Great Toe implant (Tornier, Edina, Minn.), all of which are depicted in FIG. 1B. In addition, examples of known two-component devices, which are also typically used when both the proximal phalanx and the metatarsal head are degenerated, include the Total ToeTm System (Biomet, Warsaw, Ind.); Bio-Action™ Great Toe Implant (Osteomed, Inc., Addison, Tex.); ReFlexion™ 1st MPJ Implant System (Osteomed, Inc., Addison, Tex.); and KGTI™ Kinetik Great Toe Implant System (Integra LifeSciences Corp., Plainsboro, N.J.), all of which are depicted in FIG. 1C.
Along with the knowledge in the art of numerous implant devices is the knowledge of numerous problems associated with such devices. Examples include, but are not limited to, shearing stress, loosening of the device, fragmentation, fracture through the proximal phalanx, breakage of hinged implants at the hinge, misalignment, recurrence of deformity, limited joint motion, development of plantar keratosis, development of tenderness around the joint, development of long flexor tendonitis, development of metatarsalgia, and development of metallosis. Accordingly, there is need in the art for improved implant devices for use in correcting hallux valgus. Moreover, there is need in the art for devices that are aligned and articulate in a manner consistent with natural motion of the metatarsophalangeal joint, that resist torsion forces applied to the device, and that are designed to be implanted without complex assembly, positioning, or other manipulation by the surgeon.